1. Field of the Invention
This invention relates generally to the casting of metal sheet or strip, and more particularly, to an improved method and apparatus for the casting thin metal sheets or strips in a continuous operation.
2. Background Information
The metals industry has been developing processes and apparatus for producing an as-cast product that needs little or no additional processing such as hot rolling that reduces to strip or sheet form. One such process that has arisen as a result of this development is the single or double belt thin strip casting system. In such a process, molten metal is caused to flow onto a moving horizontal surface in the form of an endless belt whereupon it solidifies as it moves along with the belt. The elongated solid strip of metal is removed from the continuous belt for further processing as desired. The endless belts used in these processes provide a substrate through which the heat of solidification is transferred. In order for the belts to have an acceptable service life, intense cooling is required. This intense cooling causes the bottom layer of the incoming liquid metal to freeze very rapidly. Consequently, any folds, oxides or other defects typically caused by the turbulence of the liquid are frozen in. In a thin gauge product, such defects may comprise an unacceptably large proportion of the strip thickness.
Another concern with moving belt systems involves the use of moving or stationary side dams which contain the lateral spreading of the molten metal. Flashing at the joint between the belts and side dams can occur resulting in edge defects in the solidified metal. In the case of stationary side dams, the molten metal may solidify and freeze to the side dam and sticking is possible which in some instances can be severe enough to cause strip separation and termination of the cast.